It uses the wp_dropdown_categories() function to display an HTML select tag populated with the taxonomy terms. (see codex for full set of arguments!) I just select all the terms I want with a simple sql statement and pass the list to the function.

However, I have found that this plugin does not save the meta field against the term if the checkbox is empty, therefore you cannot select terms that do NOT have the checkbox checked! Which is something I am also trying to achieve :/